Embodiments of the disclosure relate to diagnostic imaging, and more particularly to methods for reducing motion artifacts in shear wave measurements.
Medical diagnostic ultrasound is an imaging modality that employs ultrasound waves to probe the acoustic properties of biological tissues and produce corresponding images. Particularly, diagnostic ultrasound systems are used to visualize muscles, tendons and other internal organs to assess their size, structure and any pathological lesions using near real-time tomographic images. Further, diagnostic ultrasound also finds use in therapeutics where an ultrasound probe is used to guide interventional procedures such as biopsies.
To that end, conventional ultrasound devices include a plurality of transducer elements that convert electrical energy into mechanical energy for transmission, and mechanical energy back into electrical signals on reception. The ultrasound devices then process and transform the received electrical signals into a digital image of a target region, such as biological tissues, in near real time for facilitating further evaluation and therapy.
Recent ultrasound imaging techniques employ acoustically generated shear waves to determine the mechanical properties of biological tissues. Particularly, some of these techniques track shear wave induced displacements through a region of interest (ROI) to determine tissue mechanical properties such as shear speed and shear elastic modulus. To that end, the ultrasound devices generate shear waves in a target ROI in a corresponding phantom or actual biological tissues, for example, by delivering one or more pushing pulses. The generated shear waves cause time varying displacements while traveling from the point of generation to multiple locations along the target tissues. The ultrasound device may detect these displacements, for example, using standard Doppler tracking pulses. Particularly, tracking the shear wave induced displacements as a function of time at the multiple locations allows for shear velocity estimation, which in turn, aids in estimating one or more mechanical properties of the target tissues.
Characterization of tissue mechanical properties such as shear stiffness using shear velocity estimation has important medical applications as these properties are closely linked to tissue state with respect to pathology. Typically, at least a portion of a tissue may become stiffer than surrounding tissues indicating an onset or presence of a disease or condition such as cancer, tumor, fibrosis or steatosis.
Conventional shear velocity imaging techniques, however, suffer from probe and patient motion artifacts such as image blur, decorrelation, and groupings or stripes along the axial direction. These artifacts are more prevalent when a large ROI is generated from multiple acquisitions taken at different instants of time. The background motion will be different during the multiple acquisitions, which in turn, leads to the appearance of the striped artifacts in the shear wave displacement images.
In particular, movement of the ultrasound probe relative to the patient or internal motion such as respiration, cardiac motion, tremors and/or vibrations during the course of the multiple acquisitions can also corrupt the measured displacements. The patient's cardiac motion, for example, may cause an axial displacement of ultrasound transducers on the order of about 1.5 mm to about 6 mm during systolic and diastolic phases of the cardiac cycle. Similarly, other movements such as respiration may cause displacements of varying orders resulting in artifacts in the shear wave displacement images. Attempts to prevent appearance of motion artifacts due to background and/or patient motion using mitigating approaches such as specifically designed motion filters are often complex and require additional processing time and expense.
Thus, it is desirable to develop effective methods and systems for reducing appearance of motion artifacts during shear wave imaging. Particularly, there is a need for methods and systems that prevent, or at least substantially reduce the motion artifacts when imaging biological tissues using multiple acquisitions.